In recent years, since ink-jet recording enables to form an image simply and less expensively, it has been applied to various printing fields such as photography, various types of printing, marking, and special printing such as color filters. Specifically, by employing ink-jet recording apparatuses which eject and control minute ink droplets, ink-jet inks whose range of color reproduction, durability, and ejection adaptability have been enhanced, and paper for ink-jet printing use whose ink-absorbability, color forming properties of colorants and surface glossiness have also been markedly enhanced, it has become possible to provide an image of high quality comparable to conventional silver halide photography.
However, the ink-jet image recording system which requires special paper for ink-jet printing use causes problems such as restriction of recording media usable in the system, and a subsequent cost increase of the recording media.
On the other hand, in an office, it is growing increasingly the need of a system which enables to carry out a full color printing at high speed without receiving restriction of recording media (for example, a plain paper, a coated paper, and an art paper, etc.).
For example, about the ink-jet recording method on a plain paper, it has been performed a various investigation from the viewpoints of: printing at high speed, producing good character reproduction, no generating of the strike-through after printing (phenomenon in which the printed ink passes a recording medium and the picture image is reflected in a wire side), feathering, and a picture image smear.
As one of the methods to resolve the problems, an aqueous ink-jet ink is widely used as an ink for ink-jet. When image recording is performed on plain papers, such as a copy paper for electrophotography, a high quality paper, a medium quality paper, using such aqueous ink-jet ink, there is a problem that curling and cockling (phenomenon in which the surface of the paper becomes wrinkled after getting wet) occur on the plain paper on which carried out image recording.
On the other hand, when printing matters usually produced by offset printing, such as a leaflet, a pamphlet and a flier, are produced with an ink-jet recording method, since it is non-plate printing, reduction of cost or working steps can be realized, and printing from a small batch can be performed with on demand requirement. From this reason, an alternative machine of an offset printing machine by an ink-jet system is called for as a printing press which can perform a small batch printing or on demand printing for business use.
Usually, the coated paper for printing used for offset printing has a coated layer which consists of a white pigment and a binder, such as starch, on the back and front surfaces, by which smoothness and a feeling of gloss are increased.
In the present invention, “a coated paper” designates “a coated paper for printing used for offset printing”.
When an aqueous ink-jet ink is used for such paper and an image is formed thereon, the absorption of the aqueous ink in the coated paper is slow.
Therefore, from poor wettability of the Ink-jet ink on the surface of the coated layer, the ink will be gathered on the surface of the coated paper for printing, and there are a problem of producing a spotty pattern (or patchy pattern) and a print mottle (or uneven printing).
On the other hand, high-speed print speed is needed as a printing press which can perform a small batch printing or on demand printing. A single pass type line head ink-jet system is cited as one of the methods of realizing high-speed printing. An ink-jet head having the length more than the width of a print range is called a line head, and it is called a single pass type line head ink-jet system in which all the dots are formed when paper passes once through beneath a line head synchronizing with a paper advance.
The conventional ink-jet printing method allows to move a print head at a right angle to the direction of transportation of media and to scan. Ink dots are formed by repeating a plurality of passes which responded to the scanning width, and an image is created. This method is called a multi-pass type or a scanning type.
The scanning type ink-jet recording method performs printing by repeating a paper advance in an amount of scanning width and scanning movement of the head, while the above-mentioned line mode ink-jet printer does not require scanning movement and it can perform printing by synchronizing with a paper advance. Therefore, the line mode ink-jet printer is suitable for high-speed printing use.
When printing is carried out on a coated paper for printing with a single pass printing method, the jetted dots may cause liquid slippage due to the fact the dots will contact with adjacent dots before absorption, drying, and fixation are performed. As a result, it is hard to obtain a good image compared with the image produce with a multi-pass printing. This liquid slippage contains two steps of: changing of the dot form cause of assembling of the dots; and generating of an uneven density by mutually approaching the liquid inside of a droplet, or a high density area via a surface tension. As a result, the state of an image is deteriorated. Especially, the generating of an uneven density will yield a spotty pattern with a size of 0.1 mm-about several millimeters. Therefore, when no consideration is taken, it will generate remarkable deterioration of image.
Moreover, since the change of the dot form will occur at very short time after contact of the ejected ink dots, it was very difficult to completely prevent from generating the change. Even when the uneven density is prevented completely, due to the change of this dot form, the sharpness of a hollow character will be decreased. Furthermore, when the print pattern which has been applied an image processing especially by an error dispersion method is printed, the obtained image will have a flat shadow in which high-concentration shadow part of 50 or more was evenly printed. This originates from the following fact that the ink surrounding the hollow character of a high density area printed with an error dispersion method will come together, and a reverse dot area (a hollow portion) will be smeared away at random.
It was disclosed a method (for example, refer to Patent Document 1) for improving friction resistance by incorporating a resin neutralized with an amine in the ink so as to warm the media.
However, although this method will avoid mixture of the inks (hereafter it is called as bleeding) or liquid slippage on a non-absorptive medium to some extent, by heating and by the presence of a specific solvent, this method is still insufficient for improvement of image quality of an image produced with the single pass printing.
Moreover, it was disclosed a method (for example, refer to Patent Documents 2 to 7) in which a processing solution was applied on a recording medium before image formation is performed. When a processing solution is used and the quantity of the processing solution is increased, it will increase the aggregation property of the ink and the improvement of the image is induced by it. However, when this method was used for a coated paper for printing applied for the present invention such as a recording medium having high glossiness and low absorptivity, deteriorated glossiness and cockling were big investigational works.
The problems which should be resolves by the present invention are the followings: to avoid decrease of sharpness of an image caused by mutually assembling the dots appeared when the ink dots are printed on a coated paper for printing; and to decrease deterioration of granularity caused by ink gathering and generating the mottle of the ink density.
Further problems to be resolved are: to prevent the smear (hereafter, it is called bleeding) of the ink between the colors generated when printing is performed on the media of low absorptivity at high speed, and also to find out a good image formation method producing an image of high glossiness and good ejection property.
It is hard to achieve the improvement of sharpness of an image even by forming an image with warming a recording medium employing an ink containing a resin neutralized with an amine. This reason is considered as follows: the speed of the viscosity increasing behavior caused only by existence of a resin neutralized with an amines is insufficient for suppressing deformation of the dots produced in a single pass method; and since viscosity increase is performed on a surface of the dots, the viscosity increase has not enough power to stop the deformation of the ink dots when the ink dots are arrived at the recording medium.
Moreover, when an image is formed on a support on which the processing solution capable to aggregate that ink has been preliminarily applied, although an aggregation reaction is high, the aggregating agent will be diffused in the dots by moving from the bottom to the upward and it solidifies the upward of the dots after moving to the upward of the ink dots. The liquid of the upper part of the ink dots will be spread in a wet condition, and the liquid flowed from the adjacent ink dots are contacted, and they are combined with each other, as a consequence, the ink dots are greatly damped and spread. As a result, the effect of suppressing the decrease of sharpness is low. When an amount of a processing solution is increased, the turbulence of an image by the flow of the processing solution, and deterioration of the cockling by increase of fluid volume will occur.
When combining together a printing method using a processing solution and warming the recording medium, evaporation of a processing solution will be promoted by warming of the recording medium the after being applied with the processing solution, and the aggregation effect of the processing solution will be spoiled. For this reason, it is preferable to strike an ink immediately after the application of a processing solution.
In the scanning type printing method, it will take a long time before the ink is struck after applying a processing solution from the structure of the apparatus.
This causes deterioration of aggregation, and also deterioration of image quality, especially when the processing solution is applied on a support having low absorptivity. Because the liquid composition of the processing solution will be changed with evaporation of the liquid and the processing solution itself will exhibit repelling property.
Furthermore, the time after a processing solution is struck until ink reaches media changes greatly with the dots due to the structure of the multi-pass ejection. Therefore, there was a case where the aggregation property of the inks differed for every dot, caused lack of uniformity of the dots, and it led to deterioration of image quality.
On the other hand, in a single pass printing method, the ink dots will reach the target immediately after application of the processing solution due to the structure of the apparatus. The reaching time between the dots will be so small to become a problem. As a result, when a printing method using a processing solution and warming the recording medium are combined together, it can be said that a single pass printing method is superior to a multi-pass printing method.    Patent document 1: JP-A No. 2008-208153    Patent document 2: JP-A No. 6-092009    Patent document 3: JP-A No. 6-099576    Patent document 4: JP-A No. 6-128514    Patent document 5: JP-A No. 7-001837    Patent document 6: JP-A No. 6-057192    Patent document 7: JP-A No. 8-020161